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Wikipedia BRAS article?

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Weaver:
Referring to the Wikipedia page
        https://en.wikipedia.org/wiki/Broadband_remote_access_server

Is the penultimate paragraph, about protocols all a load of old codswallop? Or am I just losing it. (A: Quite probably the latter.  ;D )

Could anyone comment?

kitz:
Seems about right to me - The penultimate paragraph is just talking about the encapsulation protocols that could be used between the modem/router and the bRAS... and the use of VCs/VLANs
 
Putting it into BTw/Openreach speak, for example:

* 20CN the backhaul was ATM so we used PPPoA.  BTw used VP (Virtual Paths) to segment backhaul bandwidth between the DSLAMs and bRAS.
There were only 10 bRAS dotted around the UK and the backhaul network from exchange to bRAS was called MiSP.  The whole MiSP backhaul network was ATM and hence the 155/622 Mb limitations.


* NGA (FTTx) has GEA (Generic Ethernet Access) which uses PTM and PPPoE.  The cabs are connected to a Head-end exchange (not necessarily the local exchange) as Openreach has its own fibre spine that may not follow traditional E-side routing.   These head-end exchanges will most likely have its own MSE bRAS.  BTw uses S-VLANs (Service VLANs), C-VLANS (Customer VLANs) and also TVC-VLANs (TV connect/Multicast) to segment bandwidth between the exchange and GEA interconnect handover.


* 21CN WBC for ADSL2+ is slightly more diverse.  Modem connects to a C.MSAN using ATM and PPPoA... but will at some point later in the chain will connect to an F.MSAN.  When and where depends upon location. They now appear to be rolling out MSE bRAS for all WBC (not just NGA) more locally.
 
* BTw's Core uses MPLS.
Too much to explain in a couple of paras...  but more detail;-

20CN ATM Backhaul  (Bit dated now as that shows the old VPs based on 155Mbps pipes - it was originally written before wikipedia had info on such things, but it also goes into ATM, PPPoA, VPs and authentication in more depth).
BT's 21CN network - Shows the C.MSANs and F.MSANs for WBC/WBMC
BT's converged network - Shows how NGA, WBC and 20CN all slots together.  Note that image shows 21CN bRAS being at the old 20CN locations, prior to MSE bRAS. 

Weaver:
@kitz - many thanks.

I really do need to read up on this properly somehow. An SIN somewhere?

A few questions, as I'm totally confused. If Ethernet frames are being passed in CPE-to-MSAN links, are they then passed on to a BRAS (a) intact, or (b) regenerated, or (c) stripped out? (PPPoA is still supported, so BRAS servers can't rely on receiving Ethernet frames, or can they? In the PPPoA case, does an MSAN just fake some Ethernet framing up?)

What Ethernet MAC addresses are used in the frames a BRAS receives?

Weaver:
Article states
    “the BRAS is responsible for assigning network parameters such as IP addresses to the clients.”

Is that true? Certainly isn't true for me!

ejs:
On 21CN, the only ATM is over the ADSL link between CPE and MSAN. If you're using PPPoA, the ATM gets removed at the MSAN and beyond that it's Ethernet, so presumably the MSAN puts the PPP data into Ethernet frames. If you're using PPPoE over the ADSL link, because the ADSL still actually carries ATM cells, you're really doing PPPoEoA. So the MSAN still has to reassemble the data out of the ATM cell payloads anyway.

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